The present invention relates generally to the field of three-phase power distribution networks. More specifically, the invention relates to a system and method of identifying the phase of a power line in a three-phase power distribution network.
Modern power distribution systems often deliver three phase voltage to users. That is, a power line may, for example, include a plurality of conductors each designated as a specific phase of voltage. Moreover, the power distribution system may be set up to operate such that the loads of the power line are balanced (e.g., the amount of power drawn from each phase output of, for example, a three-phase transformer, is equal). However, over time, users may be added and removed from the network, which may result in an imbalance in the phase currents and voltage flow. That is, too many users may be connected to one phase of voltage while too few are connected to a second and/or third phase. This may result in a non-optimal utilization of the existing infrastructure. One manner of overcoming this load imbalance may be to institute a rebalancing of the loads, for example, by moving customers from a more highly used phase of voltage to a lesser used phase of voltage.
However, challenges exist in moving customers from one phase of voltage to another. For instance, as customers are added to and subtracted from a power distribution network, the phase of voltage that a given customer is connected to may be difficult to ascertain without costly physical tracking (typically by a worker in the field) of a given power line to the network. That is, while a load imbalance may be detected remotely, the phase to which the individual users are connected to may not be readily apparent without physically tracking the power lines from a substation to the respective user locations. Accordingly, it would be advantageous to ascertain the phase of voltage to which a user is connected to without sending a person to one or more user sites to physically determine the voltage phase being received at the various sites. Further, identifying correct phase of the loads enables differentiation between single phase and three phase faults and in turn enables the accuracy of outage management systems that rely on the phase information.
One of the methods of identifying phase is by using modems and telephone lines to establish a communication link. A signal associated with the phase at a point in the network where the phase of the line is known (the reference line) is transmitted over the communication link to a point in the network where the phase of the line is not known (the line under test). In another method, radio signals are used instead of modems and telephone lines for communication. However, both these techniques require calibration procedures and special training to be used effectively. An additional method of measuring the phase is by means of precise time stamped measurements (usually using GPS) at the substation where the phase is known and at the remote location where phase is unknown. By estimating the phase difference between the two signals, the phase at the remote location can be determined. However, this method needs two-way communications or information at two different locations to identify the phase.
Accordingly, there is a need to provide an improved apparatus and method for the identification of line phase of a power line in a power distribution network.